The present invention relates to a new construction of a veneer lathe. A conventional veneer lathe includes a cutting section made up of a knife and a stationary bar or a roller bar. A cutting power is transmitted to the cutting section through a spindle or chuck and the log itself. Known veneer lathes of the type have various drawbacks as discussed hereinbelow.
First, they are not suitable for cutting of hard logs, logs having soft cores or logs with splits and rots. If used with such a log, the chuck would only race disabling the power supply and the log would become unsuitable for use as veneer sheet. This is accounted for by the following reasons. The power supply against the high cutting resistance occurs commonly through the chuck positioned in a central area of a log. Logs grown in the South Seas and now being used for plywood generally have weak cores. A considerable force acts on part of a log where the chuck is positioned because the cutting resistance is transmitted to the core. To ensure chuck power transmission, the chuck must be pressed against opposite ends of the log with such a force which possibly break the log. Meanwhile, a log should be turned down to as is small a diameter as possible to obtain higher yield if the chuck diameter is preselected to be smaller than the intended minimum diameter of the log, but a decrease in the chuck diameter proportionally increases the probability of the chuck racing and log breakage with the consequent fall of the yield.
Second, various troubles are invited by slivers and chips of a log as well as veneer sheet which tend to become wedged between the log and the knife, between the log and the pressure bar and/or between the knife and the pressure bar. Veneer sheets cut off from a log in a wedged form will be of poor quality and in many cases be commercially unacceptable. The wedging also invites an abnormal increase in the cutting resistance and/or in the force with which the pressure bar and other press the log. Therefore, the log is very liable to be damaged unless the wedging is prevented appropriately and immediately. The above wedging phenomenon results particularly from the use of logs having rotten and/or soft spots and particularly logs having splits extending along the annual layers and those forming clearances. In addition to the degradation of the product quality and breakage of logs, the wedging will require a slow-down of the cutting operation or stoppage of the entire machine operation, bringing about a decrease of efficiency. The troubles mentioned above are showing a tendency to sharply increase.
The disadvantages of conventional veneer lathes discussed above are not only undesirable from the viewpoint of operation at factories but give rise to far more critical problems in the general field of plywood production. Since known veneer lathes are so constructed as to apply an excessively large external force to logs, logs must be suitably classified for plywood production using veneer lathes. Moreover, a number of logs are classified into grades before they are conveyed to the factories and unsuitable logs are not used for plywood production. Additionally, a large number of logs are usually classified as unsuitable in the producing districts. Thus, the material loss is serious matter and will become more prominent in the future.